Trial by LVG Rostrup in Germany shows: Inkarho® Rhododendrons are also suitable for peat-free potting soil

Inkarho® Rhododendrons prove their practical suitability in peat-free potting soil

The question of whether rhododendrons can also be successfully cultivated in peat-free substrates is more topical than ever and concerns both the horticultural trade and consumers alike. A recent trial at the Horticultural Teaching and Research Institute (LVG) Bad Zwischenahn-Rostrup of the Chamber of Agriculture of Lower Saxony with various Inkarho® Rhododendrons delivered insightful results and clearly demonstrated: the lime-tolerant varieties are very well suited for use in peat-free potting soils in home gardens.

The trial was commissioned by Inkarho® and took place between May and October 2024. Within the framework of the commissioned trial, five different varieties – including Bloombux®, the Inkarho® Fragrant Hedge ‘Lila’ and ‘Rosa’ as well as the two Easydendron® ‘English Roseum’ and ‘Junifeuer’ – were cultivated in a total of seven peat-free substrates from different suppliers. The plants were deliberately cared for as they would be in a home garden: regularly potted, fertilized and watered. In autumn, the evaluation was carried out with regard to leaf colour, growth, number of flower buds and, in particular, root development.

“The central question of whether cultivation without peat is possible can clearly be answered with ‘yes’,” explains Dipl.-Ing. Heinrich Beltz, Head of the Nursery Department at LVG Bad Zwischenahn. “The trial has shown that Inkarho® Rhododendrons can also thrive well in peat-free potting soils.” This applied to all five tested varieties.

The results varied depending on the substrate. While some soils offered optimal conditions, in other cases high pH values or unclear nutrient levels led to limitations. The general rule is: the choice of the right peat-free soil is crucial. For the peat-free cultivation of Inkarho® Rhododendrons, Beltz recommends paying particular attention to two aspects: firstly, watering, since peat-free substrates often have a lower water retention capacity, making more frequent and even irrigation important. At the same time, waterlogging must be avoided – excess water has to drain away. Secondly, nutrient supply, since depending on the initial nutrient content of the substrate, additional fertilization may be required. In principle: “Peat-free is not always the same. Each mix is different and therefore irrigation and fertilization should be adjusted accordingly. Helpful guidance is provided by the information on fertilizer packaging,” says the expert.

For sales in the horticultural trade, this means: Inkarho® Rhododendrons can also be planted by home gardeners in peat-free substrates. A corresponding note with a “peat-free tested” label is displayed on the Inkarho® Rhododendron tags. What is decisive is professional advice, to inform customers about the differences between substrates and to provide care tips. This way, demand for peat-free alternatives is actively supported without compromising on plant quality.

About INKARHO®
The Association of Lime-Tolerant Rhododendrons, INKARHO® for short, has established itself as a strong player on the market for more than 25 years. Fifteen nurseries produce a wide range of robust rhododendron varieties – from compact hedge plants such as Bloombux® to large-flowered hybrids. All varieties are characterized by high site tolerance, strong roots, healthy foliage and abundant flowers.

About LVG Rostrup
The Horticultural Teaching and Research Institute (LVG) Bad Zwischenahn-Rostrup of the Chamber of Agriculture of Lower Saxony is located in the heart of the Ammerland, one of Europe’s most important horticultural regions. As a competence centre for ornamental plant production and nurseries, it conducts practice-oriented trials and supports the horticultural profession in Northern Germany and beyond with advice and knowledge transfer.